Microstructural evolution of electrospun microfibers for biomedical applications

Thesis

The mechanical behavior and degradative properties of polymeric materials are closely tied to their microstructure. In the context of medical devices, understanding this relationship is critical for optimizing device performance and longevity. This thesis investigated how the microstructural evolution of a type of microfibrous electrospun (ES) filament evolved during the critical processing step of post-drawing. Specifically studied were filaments designed for use in knee ligament regeneration implants made from biodegradable, semicrystalline polycaprolactone (PCL). The filaments were characterized at both the fiber and molecular levels. At the fiber level, micro-computed tomography (µCT) and scanning electron microscopy (SEM) showed that stretching caused alignment, thinning, and coalescence of the fibers. At the molecular level, the crystalline microarchitecture within the fibers transformed profoundly after stretching. Techniques such as differential scanning calorimetry (DSC), 1D and 2D X-ray diffraction (XRD), and dynamic mechanical thermal analysis (DMTA) were utilized to analyze these changes. The resulting data were used to create a conceptual model of the possible mechanism for stretch-induced microstructural evolution of PCL. The proposed mechanism involves lamellar fragmentation of chain-folded crystals (CFC) and amorphous chain extension at low strains. At higher strains, CFC unfold and recrystallize into thermodynamically more stable chain-extended crystals (CEC) aligned to the stretch axis. These findings suggest potential mechanical and degradative implications for biomedical applications, warranting further investigation.

Authors: Chandler, A

• DOI: 10.5287/ora-z5kbvzeb0
• Type of award: MSc by Research
• Level of award: Masters
• Awarding institution: University of Oxford
• Language: English
• Keywords: electrospinning; poly-caprolactone; strain-induced crystallization; bio-yarn; microfibers
• Subjects: Bioengineering; Implants, artificial--biodegradation; Materials science; Polymer physics